5 files changed, 392 insertions, 40 deletions

diff --git a/weed/s3api/policy_engine/README_POLICY_ENGINE.md b/weed/s3api/policy_engine/README_POLICY_ENGINE.md
index 70dbf37f1..9a5ab3b3c 100644
--- a/weed/s3api/policy_engine/README_POLICY_ENGINE.md
+++ b/weed/s3api/policy_engine/README_POLICY_ENGINE.md
@@ -135,8 +135,70 @@ Standard AWS condition keys are supported:
 - `aws:UserAgent` - Client user agent
 - `s3:x-amz-acl` - Requested ACL
 - `s3:VersionId` - Object version ID
+- `s3:ExistingObjectTag/<tag-key>` - Value of an existing object tag (see example below)
 - And many more...
 
+### 5. Object Tag-Based Access Control
+
+You can control access based on object tags using `s3:ExistingObjectTag/<tag-key>`:
+
+```json
+{
+  "Version": "2012-10-17",
+  "Statement": [
+    {
+      "Effect": "Allow",
+      "Principal": "*",
+      "Action": "s3:GetObject",
+      "Resource": "arn:aws:s3:::my-bucket/*",
+      "Condition": {
+        "StringEquals": {
+          "s3:ExistingObjectTag/status": ["public"]
+        }
+      }
+    }
+  ]
+}
+```
+
+This allows anonymous access only to objects that have a tag `status=public`.
+
+**Deny access to confidential objects:**
+
+```json
+{
+  "Version": "2012-10-17",
+  "Statement": [
+    {
+      "Effect": "Allow",
+      "Principal": "*",
+      "Action": "s3:GetObject",
+      "Resource": "arn:aws:s3:::my-bucket/*"
+    },
+    {
+      "Effect": "Deny",
+      "Principal": "*",
+      "Action": "s3:GetObject",
+      "Resource": "arn:aws:s3:::my-bucket/*",
+      "Condition": {
+        "StringEquals": {
+          "s3:ExistingObjectTag/classification": ["confidential", "secret"]
+        }
+      }
+    }
+  ]
+}
+```
+
+**Supported Operations for Tag-Based Conditions:**
+
+Tag-based conditions (`s3:ExistingObjectTag/<key>`) are evaluated for the following operations:
+- `s3:GetObject` (GET object)
+- `s3:GetObjectVersion` (GET object with versionId)
+- `s3:HeadObject` (HEAD object)
+
+Note: For these conditions to be evaluated, the object must exist and the policy engine re-checks access after fetching the object metadata.
+
 ## Policy Evaluation
 
 ### Evaluation Order (AWS-Compatible)
@@ -270,10 +332,39 @@ go test -v -run TestPolicyValidation
 
 ## Compatibility
 
-- ✅ **Full backward compatibility** with existing `identities.json`
-- ✅ **AWS S3 API compatibility** for bucket policies
-- ✅ **Standard condition operators** and keys
-- ✅ **Proper evaluation precedence** (Deny > Allow > Default Deny)
-- ✅ **Performance optimized** with caching and compiled patterns
-
-The policy engine provides a seamless upgrade path from SeaweedFS's existing simple IAM system to full AWS S3-compatible policies, giving you the best of both worlds: simplicity for basic use cases and power for complex enterprise scenarios. 
\ No newline at end of file
+- Full backward compatibility with existing `identities.json`
+- AWS S3 API compatibility for bucket policies
+- Standard condition operators and keys
+- Proper evaluation precedence (Deny > Allow > Default Deny)
+- Performance optimized with caching and compiled patterns
+
+The policy engine provides a seamless upgrade path from SeaweedFS's existing simple IAM system to full AWS S3-compatible policies, giving you the best of both worlds: simplicity for basic use cases and power for complex enterprise scenarios.
+
+## Feature Status
+
+### Implemented
+
+| Feature | Description |
+|---------|-------------|
+| Bucket Policies | Full AWS S3-compatible bucket policies |
+| Condition Operators | StringEquals, IpAddress, Bool, DateGreaterThan, etc. |
+| `aws:SourceIp` | IP-based access control with CIDR support |
+| `aws:SecureTransport` | Require HTTPS |
+| `aws:CurrentTime` | Time-based access control |
+| `s3:ExistingObjectTag/<key>` | Tag-based access control for existing objects |
+| Wildcard Patterns | Support for `*` and `?` in actions and resources |
+| Principal Matching | `*`, account IDs, and user ARNs |
+
+### Planned
+
+| Feature | GitHub Issue |
+|---------|--------------|
+| `s3:RequestObjectTag/<key>` | For tag conditions on PUT requests |
+| `s3:RequestObjectTagKeys` | Check which tag keys are in request |
+| `s3:x-amz-content-sha256` | Content hash condition |
+| `s3:x-amz-server-side-encryption` | SSE condition |
+| `s3:x-amz-storage-class` | Storage class condition |
+| Cross-account access | Access across different accounts |
+| VPC Endpoint policies | Network-level policies |
+
+For feature requests or to track progress, see the [GitHub Issues](https://github.com/seaweedfs/seaweedfs/issues). 
\ No newline at end of file
diff --git a/weed/s3api/policy_engine/conditions.go b/weed/s3api/policy_engine/conditions.go
index fc8005fd0..4e310060a 100644
--- a/weed/s3api/policy_engine/conditions.go
+++ b/weed/s3api/policy_engine/conditions.go
@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
+	"github.com/seaweedfs/seaweedfs/weed/s3api/s3_constants"
 )
 
 // LRUNode represents a node in the doubly-linked list for efficient LRU operations
@@ -705,8 +706,36 @@ func GetConditionEvaluator(operator string) (ConditionEvaluator, error) {
 	}
 }
 
+// ExistingObjectTagPrefix is the prefix for S3 policy condition keys
+const ExistingObjectTagPrefix = "s3:ExistingObjectTag/"
+
+// getConditionContextValue resolves the value(s) for a condition key.
+// For s3:ExistingObjectTag/<key> conditions, it looks up the tag in objectEntry.
+// For other condition keys, it looks up the value in contextValues.
+func getConditionContextValue(key string, contextValues map[string][]string, objectEntry map[string][]byte) []string {
+	if strings.HasPrefix(key, ExistingObjectTagPrefix) {
+		tagKey := key[len(ExistingObjectTagPrefix):]
+		if tagKey == "" {
+			return []string{} // Invalid: empty tag key
+		}
+		metadataKey := s3_constants.AmzObjectTaggingPrefix + tagKey
+		if objectEntry != nil {
+			if tagValue, exists := objectEntry[metadataKey]; exists {
+				return []string{string(tagValue)}
+			}
+		}
+		return []string{}
+	}
+
+	if vals, exists := contextValues[key]; exists {
+		return vals
+	}
+	return []string{}
+}
+
 // EvaluateConditions evaluates all conditions in a policy statement
-func EvaluateConditions(conditions PolicyConditions, contextValues map[string][]string) bool {
+// objectEntry is the object's metadata from entry.Extended (can be nil)
+func EvaluateConditions(conditions PolicyConditions, contextValues map[string][]string, objectEntry map[string][]byte) bool {
 	if len(conditions) == 0 {
 		return true // No conditions means always true
 	}
@@ -719,11 +748,7 @@ func EvaluateConditions(conditions PolicyConditions, contextValues map[string][]
 		}
 
 		for key, value := range conditionMap {
-			contextVals, exists := contextValues[key]
-			if !exists {
-				contextVals = []string{}
-			}
-
+			contextVals := getConditionContextValue(key, contextValues, objectEntry)
 			if !conditionEvaluator.Evaluate(value.Strings(), contextVals) {
 				return false // If any condition fails, the whole condition block fails
 			}
@@ -734,7 +759,8 @@ func EvaluateConditions(conditions PolicyConditions, contextValues map[string][]
 }
 
 // EvaluateConditionsLegacy evaluates conditions using the old interface{} format for backward compatibility
-func EvaluateConditionsLegacy(conditions map[string]interface{}, contextValues map[string][]string) bool {
+// objectEntry is the object's metadata from entry.Extended (can be nil)
+func EvaluateConditionsLegacy(conditions map[string]interface{}, contextValues map[string][]string, objectEntry map[string][]byte) bool {
 	if len(conditions) == 0 {
 		return true // No conditions means always true
 	}
@@ -753,11 +779,7 @@ func EvaluateConditionsLegacy(conditions map[string]interface{}, contextValues m
 		}
 
 		for key, value := range conditionMapTyped {
-			contextVals, exists := contextValues[key]
-			if !exists {
-				contextVals = []string{}
-			}
-
+			contextVals := getConditionContextValue(key, contextValues, objectEntry)
 			if !conditionEvaluator.Evaluate(value, contextVals) {
 				return false // If any condition fails, the whole condition block fails
 			}
diff --git a/weed/s3api/policy_engine/engine.go b/weed/s3api/policy_engine/engine.go
index 01af3c240..62e375eff 100644
--- a/weed/s3api/policy_engine/engine.go
+++ b/weed/s3api/policy_engine/engine.go
@@ -91,6 +91,14 @@ func (engine *PolicyEngine) DeleteBucketPolicy(bucketName string) error {
 	return nil
 }
 
+// HasPolicyForBucket checks if a bucket has a policy configured
+func (engine *PolicyEngine) HasPolicyForBucket(bucketName string) bool {
+	engine.mutex.RLock()
+	defer engine.mutex.RUnlock()
+	_, exists := engine.contexts[bucketName]
+	return exists
+}
+
 // EvaluatePolicy evaluates a policy for the given arguments
 func (engine *PolicyEngine) EvaluatePolicy(bucketName string, args *PolicyEvaluationArgs) PolicyEvaluationResult {
 	engine.mutex.RLock()
@@ -154,7 +162,7 @@ func (engine *PolicyEngine) evaluateStatement(stmt *CompiledStatement, args *Pol
 
 	// Check conditions
 	if len(stmt.Statement.Condition) > 0 {
-		if !EvaluateConditions(stmt.Statement.Condition, args.Conditions) {
+		if !EvaluateConditions(stmt.Statement.Condition, args.Conditions, args.ObjectEntry) {
 			return false
 		}
 	}
@@ -201,10 +209,8 @@ func ExtractConditionValuesFromRequest(r *http.Request) map[string][]string {
 		values["aws:Referer"] = []string{referer}
 	}
 
-	// S3 object-level conditions
-	if r.Method == "GET" || r.Method == "HEAD" {
-		values["s3:ExistingObjectTag"] = extractObjectTags(r)
-	}
+	// Note: s3:ExistingObjectTag/<key> conditions are evaluated using objectEntry
+	// passed to EvaluatePolicy, not extracted from the request.
 
 	// S3 bucket-level conditions
 	if delimiter := r.URL.Query().Get("delimiter"); delimiter != "" {
@@ -243,13 +249,6 @@ func ExtractConditionValuesFromRequest(r *http.Request) map[string][]string {
 	return values
 }
 
-// extractObjectTags extracts object tags from request (placeholder implementation)
-func extractObjectTags(r *http.Request) []string {
-	// This would need to be implemented based on how object tags are stored
-	// For now, return empty slice
-	return []string{}
-}
-
 // BuildResourceArn builds an ARN for the given bucket and object
 func BuildResourceArn(bucketName, objectName string) string {
 	if objectName == "" {
@@ -352,15 +351,6 @@ func GetObjectNameFromArn(arn string) string {
 	return ""
 }
 
-// HasPolicyForBucket checks if a bucket has a policy
-func (engine *PolicyEngine) HasPolicyForBucket(bucketName string) bool {
-	engine.mutex.RLock()
-	defer engine.mutex.RUnlock()
-
-	_, exists := engine.contexts[bucketName]
-	return exists
-}
-
 // GetPolicyStatements returns all policy statements for a bucket
 func (engine *PolicyEngine) GetPolicyStatements(bucketName string) []PolicyStatement {
 	engine.mutex.RLock()
diff --git a/weed/s3api/policy_engine/engine_test.go b/weed/s3api/policy_engine/engine_test.go
index 1bb36dc4a..4de537ac1 100644
--- a/weed/s3api/policy_engine/engine_test.go
+++ b/weed/s3api/policy_engine/engine_test.go
@@ -5,9 +5,23 @@ import (
 	"net/url"
 	"testing"
 
+	"github.com/seaweedfs/seaweedfs/weed/s3api/s3_constants"
 	"github.com/seaweedfs/seaweedfs/weed/s3api/s3err"
 )
 
+// tagsToEntry converts a map of tag key-value pairs to the entry.Extended format
+// used for s3:ExistingObjectTag/<key> condition evaluation
+func tagsToEntry(tags map[string]string) map[string][]byte {
+	if tags == nil {
+		return nil
+	}
+	entry := make(map[string][]byte)
+	for k, v := range tags {
+		entry[s3_constants.AmzObjectTaggingPrefix+k] = []byte(v)
+	}
+	return entry
+}
+
 func TestPolicyEngine(t *testing.T) {
 	engine := NewPolicyEngine()
 
@@ -714,3 +728,233 @@ type MockLegacyIAM struct{}
 func (m *MockLegacyIAM) authRequest(r *http.Request, action Action) (Identity, s3err.ErrorCode) {
 	return nil, s3err.ErrNone
 }
+
+// TestExistingObjectTagCondition tests s3:ExistingObjectTag/<tag-key> condition support
+func TestExistingObjectTagCondition(t *testing.T) {
+	engine := NewPolicyEngine()
+
+	// Policy that allows GetObject only for objects with specific tag
+	policyJSON := `{
+		"Version": "2012-10-17",
+		"Statement": [
+			{
+				"Effect": "Allow",
+				"Principal": "*",
+				"Action": "s3:GetObject",
+				"Resource": "arn:aws:s3:::test-bucket/*",
+				"Condition": {
+					"StringEquals": {
+						"s3:ExistingObjectTag/status": ["public"]
+					}
+				}
+			}
+		]
+	}`
+
+	err := engine.SetBucketPolicy("test-bucket", policyJSON)
+	if err != nil {
+		t.Fatalf("Failed to set bucket policy: %v", err)
+	}
+
+	tests := []struct {
+		name       string
+		objectTags map[string]string
+		expected   PolicyEvaluationResult
+	}{
+		{
+			name:       "Matching tag value - should allow",
+			objectTags: map[string]string{"status": "public"},
+			expected:   PolicyResultAllow,
+		},
+		{
+			name:       "Non-matching tag value - should be indeterminate",
+			objectTags: map[string]string{"status": "private"},
+			expected:   PolicyResultIndeterminate,
+		},
+		{
+			name:       "Missing tag - should be indeterminate",
+			objectTags: map[string]string{"other": "value"},
+			expected:   PolicyResultIndeterminate,
+		},
+		{
+			name:       "No tags - should be indeterminate",
+			objectTags: nil,
+			expected:   PolicyResultIndeterminate,
+		},
+		{
+			name:       "Empty tags - should be indeterminate",
+			objectTags: map[string]string{},
+			expected:   PolicyResultIndeterminate,
+		},
+		{
+			name:       "Multiple tags with matching one - should allow",
+			objectTags: map[string]string{"status": "public", "owner": "admin"},
+			expected:   PolicyResultAllow,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			args := &PolicyEvaluationArgs{
+				Action:      "s3:GetObject",
+				Resource:   "arn:aws:s3:::test-bucket/test-object",
+				Principal:  "*",
+				ObjectEntry: tagsToEntry(tt.objectTags),
+			}
+
+			result := engine.EvaluatePolicy("test-bucket", args)
+			if result != tt.expected {
+				t.Errorf("Expected %v, got %v", tt.expected, result)
+			}
+		})
+	}
+}
+
+// TestExistingObjectTagConditionMultipleTags tests policies with multiple tag conditions
+func TestExistingObjectTagConditionMultipleTags(t *testing.T) {
+	engine := NewPolicyEngine()
+
+	// Policy that requires multiple tag conditions
+	policyJSON := `{
+		"Version": "2012-10-17",
+		"Statement": [
+			{
+				"Effect": "Allow",
+				"Principal": "*",
+				"Action": "s3:GetObject",
+				"Resource": "arn:aws:s3:::test-bucket/*",
+				"Condition": {
+					"StringEquals": {
+						"s3:ExistingObjectTag/status": ["public"],
+						"s3:ExistingObjectTag/tier": ["free", "premium"]
+					}
+				}
+			}
+		]
+	}`
+
+	err := engine.SetBucketPolicy("test-bucket", policyJSON)
+	if err != nil {
+		t.Fatalf("Failed to set bucket policy: %v", err)
+	}
+
+	tests := []struct {
+		name       string
+		objectTags map[string]string
+		expected   PolicyEvaluationResult
+	}{
+		{
+			name:       "Both tags match - should allow",
+			objectTags: map[string]string{"status": "public", "tier": "free"},
+			expected:   PolicyResultAllow,
+		},
+		{
+			name:       "Both tags match (premium tier) - should allow",
+			objectTags: map[string]string{"status": "public", "tier": "premium"},
+			expected:   PolicyResultAllow,
+		},
+		{
+			name:       "Only status matches - should be indeterminate",
+			objectTags: map[string]string{"status": "public"},
+			expected:   PolicyResultIndeterminate,
+		},
+		{
+			name:       "Only tier matches - should be indeterminate",
+			objectTags: map[string]string{"tier": "free"},
+			expected:   PolicyResultIndeterminate,
+		},
+		{
+			name:       "Neither tag matches - should be indeterminate",
+			objectTags: map[string]string{"status": "private", "tier": "basic"},
+			expected:   PolicyResultIndeterminate,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			args := &PolicyEvaluationArgs{
+				Action:      "s3:GetObject",
+				Resource:   "arn:aws:s3:::test-bucket/test-object",
+				Principal:  "*",
+				ObjectEntry: tagsToEntry(tt.objectTags),
+			}
+
+			result := engine.EvaluatePolicy("test-bucket", args)
+			if result != tt.expected {
+				t.Errorf("Expected %v, got %v", tt.expected, result)
+			}
+		})
+	}
+}
+
+// TestExistingObjectTagDenyPolicy tests deny policies with tag conditions
+func TestExistingObjectTagDenyPolicy(t *testing.T) {
+	engine := NewPolicyEngine()
+
+	// Policy that denies access to objects with confidential tag
+	policyJSON := `{
+		"Version": "2012-10-17",
+		"Statement": [
+			{
+				"Effect": "Allow",
+				"Principal": "*",
+				"Action": "s3:GetObject",
+				"Resource": "arn:aws:s3:::test-bucket/*"
+			},
+			{
+				"Effect": "Deny",
+				"Principal": "*",
+				"Action": "s3:GetObject",
+				"Resource": "arn:aws:s3:::test-bucket/*",
+				"Condition": {
+					"StringEquals": {
+						"s3:ExistingObjectTag/classification": ["confidential"]
+					}
+				}
+			}
+		]
+	}`
+
+	err := engine.SetBucketPolicy("test-bucket", policyJSON)
+	if err != nil {
+		t.Fatalf("Failed to set bucket policy: %v", err)
+	}
+
+	tests := []struct {
+		name       string
+		objectTags map[string]string
+		expected   PolicyEvaluationResult
+	}{
+		{
+			name:       "No tags - allow by default statement",
+			objectTags: nil,
+			expected:   PolicyResultAllow,
+		},
+		{
+			name:       "Non-confidential tag - allow",
+			objectTags: map[string]string{"classification": "public"},
+			expected:   PolicyResultAllow,
+		},
+		{
+			name:       "Confidential tag - deny",
+			objectTags: map[string]string{"classification": "confidential"},
+			expected:   PolicyResultDeny,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			args := &PolicyEvaluationArgs{
+				Action:      "s3:GetObject",
+				Resource:   "arn:aws:s3:::test-bucket/test-object",
+				Principal:  "*",
+				ObjectEntry: tagsToEntry(tt.objectTags),
+			}
+
+			result := engine.EvaluatePolicy("test-bucket", args)
+			if result != tt.expected {
+				t.Errorf("Expected %v, got %v", tt.expected, result)
+			}
+		})
+	}
+}
diff --git a/weed/s3api/policy_engine/types.go b/weed/s3api/policy_engine/types.go
index d68b1f297..c6c76b55f 100644
--- a/weed/s3api/policy_engine/types.go
+++ b/weed/s3api/policy_engine/types.go
@@ -106,6 +106,11 @@ type PolicyEvaluationArgs struct {
 	Resource   string
 	Principal  string
 	Conditions map[string][]string
+	// ObjectEntry is the object's metadata from entry.Extended.
+	// Used for evaluating conditions like s3:ExistingObjectTag/<tag-key>.
+	// Tags are stored with s3_constants.AmzObjectTaggingPrefix (X-Amz-Tagging-) prefix.
+	// Can be nil for bucket-level operations or when object doesn't exist.
+	ObjectEntry map[string][]byte
 }
 
 // PolicyCache for caching compiled policies